Automotive manufacturers are currently utilizing camless intake and exhaust valve assemblies to control fluid communication in engine cylinders of internal combustion engines. The camless valve assemblies may utilize hydraulic, pneumatic, or electromechanical means to move a valve.
It is further known that varying an engine valve dwell time (i.e., the time interval a valve is open), a valve dwell position (i.e., the amount the valve is open), a valve opening rate, a valve closing rate, and an initial opening time of a valve (i.e., valve phasing) may be used to increase fuel efficiency and lower emissions. Further, the most flexible valve assemblies may be independently actuated/controlled with respect to other valve assemblies in an engine.
Referring to FIG. 1, a known engine 10 having an engine head 12 and electromechanical valve assemblies 14, 16 is shown. The engine head 12 includes an air intake line 18 and an exhaust line 20. The valve assemblies 14, 16 control communication between the line 18, 20, respectively, with an engine cylinder (not shown).
The valve assembly 14 includes a pair of solenoids 22, 24, and a valve 26. The valve 26 includes a valve stem 28 and a valve head 30. The solenoids 22, 24 are utilized to either open or close the valve 26. In particular, when the solenoid 24 is energized (and solenoid 22 is de-energized), the valve head 30 is moved axially away from a valve seat 32 to allow fluid communication between the intake line 18 and a cylinder (not shown). When the solenoid 22 is energized (and solenoid 24 is de-energized) the valve head 30 engages the valve seat 32 to prevent fluid communication between the intake line 18 and the cylinder. Thus, the known valve assembly 14 has a two-position valve 26 having either a full open state or a full closed state. As such, the valve assembly 14 has several operational disadvantages. In particular, the valve assembly 14 cannot precisely control a valve dwell time duration, a valve dwell position, a valve opening rate, a valve closing rate, valve phasing. Thus, the valve assembly 14 cannot be utilized to effectively increase fuel efficiency and lower emissions in an engine. Further, the valve assembly 14 does not provide for soft seating of the valve head 30 on the valve seat 32 under all operating conditions of the engine including temperature extremes and control strategy variations. As a result, the valve head 30 generates undesirable noise when contacting the valve seat 32.
Another known electromechanical valve assembly (not shown) includes an electric motor, a cam, and a poppet valve. The motor selectively rotates an output shaft that is connected to the cam. The cam converts that rotary motion of the output shaft to an axial motion of the poppet valve. This known valve assembly is capable of controlling a valve dwell time, a valve dwell position, a valve opening rate, and a valve closing rate. However, the known valve assembly suffers from several disadvantages. First, the valve assembly requires a separate cam resulting in increased component and manufacturing costs. Further, the valve assembly requires a relatively large package space since a separate cam is utilized for each poppet valve.